1. Field of the Invention
The invention relates generally to blowout preventers used in the oil and gas industry. Specifically, the invention relates to a blowout preventer with a novel shear load intensifying mechanism.
2. Background Art
Well control is an important aspect of oil and gas exploration. When drilling a well, for example, in oil and gas exploration applications, devices must be put in place to prevent injury to personnel and equipment associated with the drilling activities. One such well control device is known as a blowout preventer (“BOP”).
BOP's are generally used to seal a wellbore in the event of a “blowout.” For example, drilling wells in oil or gas exploration involves penetrating a variety of subsurface geologic structures, called “formations” or “layers.” Each layer generally comprises a specific geologic composition such as, for example, shale, sandstone, limestone, etc. Each layer may contain trapped fluids or gas at different formation pressures, and the formation pressures generally increase with increasing depth. The working pressure of the drilling fluid in the wellbore is generally adjusted to at least balance the formation pressure by, for example, increasing a density of the drilling fluid in the wellbore or increasing pump pressure at the surface of the well.
There are occasions during drilling operations when a wellbore may penetrate a layer having a formation pressure substantially higher that the pressure maintained in the wellbore. When this occurs, the well is said to have “taken a kick.” The pressure increase associated with the kick is generally produced by an influx of formation fluids (which may be a liquid, a gas, or a combination thereof) into the wellbore. The relatively high pressure kick tends to propagate from a point of entry in the wellbore uphole (from a high pressure region to a low pressure region). If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. These “blowouts” often result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and in substantial injury or death of rig personnel.
Because of the risk of blowouts, BOP's are typically installed at the surface or on the sea floor in deep water drilling arrangements so that kicks may be adequately controlled and “circulated out” of the system. BOP's may be activated to effectively seal in a wellbore until measures can be taken to control the kick. There are several types of BOP's, the most common of which are annular blowout preventers and ram-type blowout preventers.
Annular blowout preventers typically comprise annular elastomer “packers” that may be activated (e.g., inflated) to encapsulate drillpipe and well tools and completely seal the wellbore. A second type of the blowout preventer is the ram-type blowout preventer. Ram-type preventers typically comprise a body and at least two oppositely disposed bonnets.
Interior of each bonnet is a piston actuated ram. The rams may be pipe rams (or variable pipe rams) (which, when activated, move to engage and surround drillpipe and well tools to seal the wellbore), shear rams (which, when activated, move to engage and physically shear any drillpipe or well tools in the wellbore), or blind rams. The rams are typically located opposite of each other and, whether pipe rams or shear rams, the rams typically seal against one another proximate a center of the wellbore in order to completely seal the wellbore.
In some cases, flexible materials that are located within a central bore of a BOP will “snake” around the shearing elements on shear rams. When this occurs, the flexible materials may not be fully sheared by the rams when the BOP is energized and the rams closed. Thus, what is needed is a BOP with ram blocks that will effectively shear both rigid and flexible materials that are located in a central bore of the BOP.